Disable auto-dimming? (ambient light sensor)

Scott in AZ said:

My ambient sensor is failed so my headlights are on all the time, and DRL are never on. I’m getting psyched up to remove the dash, paint it with a Pewter refresh, and replace the ambient sensor.

I think if you ground out your sensor, your DRLs won’t work, and you’ll have same problem as I do.

Then the only other electrical gremlin I’ll have is the fuel gage. My level sensor is starting to fail. Fuel Gage measures accurately below 3/4 tank but intermittent goes to “E” empty when full. I’ve heard I need to replace the fuel pump to fix this.

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If it's the same as the trucks, yes, the fuel pump and sending unit are all together. Trucks are easier because you can lift the bed and get to it. Guessing the tank will need to be lowerd on these for replacement.

Any possibility it's the cluster? (Might be worth checking so you don't have to drop the tank)
Or it maybe a good time to put a new fuel pump in anyway..

For light sensor, I'm thinking about using a relay like this..


Wire it so sensor is connected when headlights are on. (So it dims at night and dimmer adjustment works, otherwise daytime it's full brightness no dimmer control)

But you still need a sensor that works..

quick test seems to show

15k ohm resistance in dark area
500 ohm resistance in direct sunlight.

Makes sense why GM tells you to wire in a 600ohm resistor to disable auto headlights.

(white wire is signal and black/white is ground)
Thinking I might wire those pins to a relay and resistors..

Scott in AZ said:

Foggy if this works Ima’ come correct w you. Thanks already. I’ll give it a try and let you know.

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It's the sulpher in the fuel that builds up on the sensor. C5 corvettes are really bad about this..
but it applies to a bunch of diff vehicles. Hope it works for you !!

Little update, a 10K ohm resistor will put the interior lights into night mode. Dimmer can adjust!
Next step is to wire up a relay so when lights turn on, interior lights will dim.

UPDATE: I used a 680ohm for daytime, 10k ohm for switched using a switching (SPDT) relay and wired the relay trigger to the park lamp circuit (brown wire, but I used the trailer park lamp fuse) Still about a 3 second delay before display dims when turning on lights, I guess that is programmed so the display isnt dimming at every little shadow..

IMPORTANT: Without a diode, there is a voltage spike that will cause your BCM to turn off the display backlighting for a second when turning off the lights (and therefore the relay)
So make if you do this, you get a relay with diode built in, or wire one yourself to the coil connections on the relay.

update2: well maybe its not a reverse voltage spike.
Installed a relay with diode, and when turning headlights off, the gauge backlighting still turns off for 2-3 seconds before turning back on in daylight setting.
The dic display does not have this quirk, only the gauge lighting. Also does it when I disconnect the daytime resistor and leave that circuit open (simulating a missing light sensor)
Reverted back to the sensor for now, afraid the signal is bad and I might fry something.

If anyone has an idea why the BCM would turn gauge backlight off for a couple seconds, when turning off lights and switching from 10k ohm to 680 ohm resistor on the light sensor to ground circuit, please let me know! Wiring diagram says it is an analog/digital pull-up

UPDATE: When the headlights and auto lights are off (with the stock ambient light sensor), and it is dark outside, the gauge backlighting is off. I believe that is the reason my gauge lighting would go off as I changed from lights on to lights off, the 3 second delay before changing backlighting modes. It would first change from nighttime mode/lights on to nighttime mode/lights off, before finally changing to daytime mode. Will re-install the relay in the near future.